Method and apparatus for deep-drawing sheet metal plates



June 24, 1969 p REGELMAYER ET AL 3,451,239

METHOD AND APPARATUS FOR DEEP-DRAWING SHEET METAL PLATES Filed 001;. 4, 1965 INVENTORS PETER RIEGELMAYER 'HELMUT TURK BY 96C) ATTORNEYS United States Patent Int. Cl. B513 5/04 US. Cl. 72-56 12 Claims ABSTRACT OF THE DISCLOSURE A method and an apparatus for the free expansion explosive forming of sheet metal wherein the explosive is nonuniformly areally distributed over the surface of the sheet metal to form a correspondingly nonuniformly shaped product.

Background of the invention As is known, very large energy quantities can be produced by means of explosives. Use is made of this fact already for some considerable time in the manner that for purposes of deep-drawing of sheet metal parts in lieu of large, heavy and expensive presses, explosives are oftentimes used. The arrangement heretofore has been made in such a manner that the sheet metal part to be deformed is clamped into a correspondingly shaped matrix or die, arranged on the bottom of a container open on top and filled with a transmitting medium, preferably water, or is inserted into or placed upon a correspondingly shaped form or die and the hollow space present below the sheet metal part is evacuated as well as the explosive is arranged centrally above the sheet metal part within the transmission medium in the form of one or also several concentrated charges, and at a distance from the sheet metal part to be deformed determined in dependence on the material and dimensions thereof, whereby the transmission medium, on the one hand, has the task to transmit the pressure of the detonating explosive uniformly onto the sheet metal part, and on the other, serves to weaken the brisant and highly explosive effect of the explosive on the sheet metal part, i.e., to protect the latter against damage or destruction.

Since the effect of the explosive on the sheet metal part to be deformed is determined, as also known, by the density of the transmission medium; namely, is the greater the larger the density of the transmission medium, one is thus in a position to influence favorably by selection of a transmission medium of correspondingly large density the required explosive quantity; that is, to be able to get along with a relatively small amount of explosive. Thus, one necessitates, for example, with a deformation in water, in addition to which also incompressible gels, sand, chalk and many other inert materials may be used as transmission medium, approximately one half the amount of explosive than under otherwise equal conditions with a free deformation in air. However, it is disadvantageous with the known arrangements of the explosive in the form of concentrated charges that of such a concentrated charge only a very small portion; namely, an approximately sector-shaped portion directed toward the sheet metal part to be deformed, becomes effective directly in the sense of the desired deformation of the sheet metal part. Since the predominant part of the utilized explosive is thus lost unused for the deformation of the sheet metal part, a relatively large explosive quanity is necessary even if use is made of the aforementioned possibility of the utilization of a transmission ice medium having a high density. Furthermore, of disadvantage with the known arrangement of the explosive in the form of concentrated charges is also the nonuniform distance thereof from the individual areas or regions of the sheet metal part to be deformed and especially the relatively large extent necessarily resulting therefrom of the explosive charge in a direction perpendicular to the plane of the sheet metal part to be deformed. Since the effect of an explosive depends also, as is known, from its layer thickness and is the larger the thicker the explosive layer, the explosive charge has to be arranged at a relatively large distance from the sheet metal part for purposes of achieving a sufficient protection of the sheet metal part to be deformed against the highly explosive and brisant effect of the explosive. Since with the known prior art method of deep-drawing by means of an explosive, the explosive charge is arranged completely within the transmission medium, this also requires accordingly a relatively large amount of transmission medium as well as in particular with sheet metal parts or plates of large thickness and dimensions, large and expensive containers or vessels for accommodating the same.

Summary of the invention It has now been discovered that the aforementioned disadvantages may be avoided with the deep-drawing of sheet metal parts by means of explosives, if according to the teachings of the present invention, the explosive is arranged above the sheet metal part, while leaving a hollow space therebelow which corresponds in size at least to the form and shape to be achieved and resting with its rim on a base plate or support, in the manner of an areal distribution extending at least up to the inner rim of the base support. Owing to the distribution of the explosive over a relatively large area not only a very much larger proportion of the explosive becomes effective directly in the sense of the intended deformation of the sheet metal part, but additionally one also arrives at a relatively small thickness of the explosive layer, which permits to come relatively close to the sheet metal part with the explosive without running the risk that the sheet metal part suffers damage by the highly explosive and brisant effect of the explosive. Consequently, one can get along with the explosive arrangement according to the present invention with relatively little transmission medium. This in turn permits to keep the container or vessel for receiving the transmission medium relatively low insofar as use is made at all of such a container and, for example, the aforementioned prior art arrangement is used in which the sheet metal part to be deformed is clamped into a matrix or die arranged on the bottom of a container filled with transmission medium or is inserted into or placed on a corresponding form or die. However, the present invention preferably also contemplates to dispense both with the use of a matrix and with the use of a container as well as of a transmission medium, for example, water, sand or the like, which makes the container necessary, and to so make the arrangement that the sheet metal part to be deformed is placed only loosely on a base support and a more or less thick layer of inert material such as cardboard, rubber, or the like, is at first laid upon the sheet metal part, and the explosive is thereafter mounted in corresponding distribution on the layer of inert material. The inert material then no longer performs the function of a transmission medium, in its proper sense, but it merely serves the purpose to protect the sheet metal part against the highly explosive and brisant effect of the explosive.

As can be readily proved by experiments and tests, it sufiices completely for the realization of the method in accordance with the present invention if a recess corresponding to the deformation of the sheet metal part to be achieved is formed, for instance into the sand and the sheet metal part, together with the inert material and the explosive, is loosely placed upon this sand form or mold, whereby an evacuating of the space disposed below the sheet metal part is obviated since the sand form is sufiiciently porous in order to permit an escape of the air present below the sheet metal part. It could even be further established on the basis of these tests that no form, die or mold at all is necessary for the realization of the method in accordance with the present invention but instead that it is possible to achieve the desired deformation if the sheet metal part is placed with its rim merely upon a ring-shaped base support provided with a sufficiently large hollow space disposed therebelow and the explosive is arranged over the sheet metal part in a distribution corresponding to the desired deformation. It is only necessary in connection therewith to absorb relatively softly the deformed sheet metal part which is accelerated during the detonation of the explosive and is thrown or thrust in the downward direction through the ring-shaped support so that the sheet metal part does not subsequently suffer any damage for example by an excessively hard impact.

It is additionally proposed in accordance with a further appropriate development of the method in accordance with the present invention, in the sense of a requirement for as small as possible an amount of inert material, to utilize an explosive whose detonation velocity is smaller than the velocity of the sound in the sheet metal part to be deformed. The result thereby becomes the more favorable, the larger the difference between the detonation velocity of the explosive and the velocity of the sound in the sheet metal part. If, according to a further teaching in accordance with the present invention, an explosive is used whose detonation velocity does not exceed that of the shearing and/ or transversal wave in the sheet metal part to be deformed, then any arrangement of inert material between the sheet metal part and the explosive may be dispensed with altogether, i.e., the explosive which may be in powder, plastic or gelatinous form, may be arranged directly on the sheet metal part without danger of an eventual damage of the sheet metal part, for example, twin formation or intercrystalline corrosion susceptibility, whence in combination with the use of, for example, a sand form, even with sheet metal parts of large surfaces and great thickness a very simple and inexpensive method of deforming becomes available.

Depending on the desired degree of deformation of the sheet metal part and also on the ratio of the surface extent thereof to its thickness in a given case, a drawing ring or die is provided between the base support and the sheet metal part whereby it is, of course, also possible without any difiiculty to make the drawing die in one piece with the base support; that is, to form the desired and required drawing radius into the base support. If, however, the drawing die is made separately by itself, then it suffices to insert the same loosely between the sheet metal part and the base support. However, in order to insure also a good support of the sheet metal rim, it is recommended in connection therewith to make the outer dimensions of the drawing die at least equally large as the outer dimensions of the sheet metal part.

In order to prevent with certainty a wrinkling during the deformation with thin and very thin sheet metal parts, for example, with those having a thickness of about 3 mm. or less, it is appropriate to arrange between the sheet metal part and the inert material or explosive a flat metallic ring of preferably about 1.5 to 2 times the thickness of the sheet metal part to be deformed which serves as annular antiwrinkle holder. Also in this case, a fastening or securing is not necessary if care is taken that the annular holder is kept down during the deformation operation by the detonation pressure of the explosive, which can be achieved, both with the use of a transmission medium as also in case when the explosive is so placed on the sheet metal part either with or without the use of an inert intermediate layer that the explosive is disposed at least in part over the radial extent of the ring, whose outer dimensions are again made appropriately at least equally large as the outer dimensions of the sheet metal part so that also a warping or wrinkling is avoided with certainty along the outer rim of the sheet metal part. It has also proved itself as favorable and appropriate in connection therewith if the inner dimension of the annular holder is constructed so as to correspond accurately to that of the drawing die whereby the inner area of the annular holder abuts during the deformation operation against the drawing radius and forms, together with the drawing die, a gap of uniform width through which the sheet metal part can slide smoothly and without any wrinkling.

In order to achieve in case of use of an annular antiwrinkle holder a completely plane and smooth abutment surface for the explosive and especially also in order to achieve that within the inner space of the annular holder no explosive is present whose radially directed detonation effect might have as a consequence the busting open or cracking of the annular holder, insofar as the latter is placed directly on the sheet metal part, i.e., without use of a transmission medium and also without use of an inert material serving for the protection of the sheet metal part against the brisant effect of the explosive, it is recommended to fill the recessed, inwardly disposed space of the annular holder with an inert material, for example, with cardboard, rubber or the like whereby it is again expressly noted that this inert material serves exclusively for purposes of level equalization for the abutment of the explosive but no other purpose.

With sheet metal parts of less than 2 mm. in thickness it may occasionally happen even with the use of an explosive whose detonation velocity does not exceed the velocity of the shearing and/or transverse wave in the sheet metal part to be deformed, i.e., which would normally permit a direct placemetn of the explosive on the sheet metal part to be deformed, especially when the explosive is used in powder form, that for purposes of achieving a completely satisfactory detonation the thickness of the explosive layer has to be maintained larger than would be necessary as such for the desired deformation of the sheet metal part. In order to prevent in such a case an excessively strong effect of the explosive on the sheet metal part, an inert material of corresponding thickness has to be arranged in that case over the entire surface between the sheet metal part and the explosive. Insofar an an annular anti-wrinkle holder is provided in that case, the latter is made of such thickness that no further inert material needs to be assembled in addition to the inert material necessary alerady present for the level equalization. However, also in this case it is again to be noted expressly that the inert material does not have to fulfill the function of a transmission medium and that there is no need in connection therewith of any particular securing or clamping means of the parts, i.e., also in this case, for example, the matrix or form necessary and customary heretofore may be dispensed with. Furthermore, a possibility is hereby also given for dispensing with the arrangement of inert intermediate layers by the fact that several of these thin sheet metal parts can be arranged one above the other and can be deformed together simultaneously.

Moreover, the method in accordance with the present invention, whose main field of application is the deepdrawing of sheet metal parts difficult to deform and made of material with high rigidity and/or large thickness is obviously not limited to the use of uniformly thick explosive layers. Instead, it is within the scope and spirit of the present invention, to utilize also explosive layers having a thickness differing over the entire surface thereof, for example, for manufacturing asymmetric shapes, whereby the desired or required differing deformation degrees can be readily achieved by the non-uniformly thick explosive layer-of course as constructed in a predetermined manner.

Accordingly, it is an object of the present invention to provide a method for deep-drawing sheet metal parts which is simple, easy to use, and reliable in operation yet avoids the aforementioned short-comings and drawbacks encountered with the prior art methods.

Another object of the present invention resides in a deep-drawing method for sheet metal parts by means of explosives which obviates the need for large, expensive and heavy presses.

A further object of the present invention resides in a method of deep-drawing sheet metal parts which utilizes the explosive in a greatly improved and vastly more effective manner than possible heretofore.

Still another object of the present invention resides in a method for deep-drawing sheet metal parts by means of explosives which prevents wrinkling and/ or warping of the sheet metal parts during the deformation theerof.

Another object of the present invention resides in a method for deep-drawing sheet metal parts and in an apparatus for carrying out the method which protects the sheet metal parts against damage, yet obviates the need for expensive structures, a transmission medium used within the structures and/ or expensive dies or matrices.

Still a further object of the present invention resides in a method for deep-drawing sheet metal parts and in an apparatus for carrying out the method which reduces the amount of explosives that has to be used.

Brief description of the drawing These and other objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawing which shows, for purposes of illustration only, one arrangement for carrying out the method in accordance with the present invention, and wherein:

The single figure is a somewhat schematic cross-sectional view through an arrangement for carrying out the method in accordance with the present invention.

Detailed description of the drawing Referring now to the single figure of the drawing, the form or shape 8 to be achieved, in the illustrated embodiment a hemisphere, indicated in dash lines is formed within sand 7 inside of the drawing die 6 placed upon the sand 7 on which is loosely placed the sheet metal part 5 to be deformed. The antiwrinkle annular holder 4 is placed on the sheet metal part 5 which may be in the form of a disk. For purposes of equalizing the level, the interior recess within the annular holder 4 is filled by means of the inert material 3, for example, of cardboard placed upon the sheet metal disk 5 and terminating fiush with the upper surface of the annular holder 4.

The explosive 2 is distributed in a uniformly thick layer over the entire surface of the disk 5 on the inert material 3 and on the annular holder 4 whose outer diameter coincides with that of the sheet metal part 5 and whose inner diameter corresponds to that of the drawing die 6. The explosive charge 2 is provided in the center of the disk 5 with a conventional primer or detonator 1.

Upon ignition of the explosive 2 means of the primer 1 an acceleration is imparted to the sheet metal part 5 suflicient for the desired deformation thereof into the hemispherical shape; the thus-accelerated sheet metal part 5 is again decelerated within the sand 7 without strong impact.

The sheet metal body thus deformed into a hemisphere may, if desired, be calibrated subsequently in any .conventional manner, for example, by the conventional method of calibrating which utilizes an explosive and transmission medium into an accurate, desired dimension.

While we have shown and described one embodiment in accordance with the present invention, it is understood that the same is not limited thereto but is susceptible of numerous changes and modifications as known to a person skilled in the art and we therefore do not wish to be limited to the details shown and described herein but intend to cover all such changes and modifications as are encompassed by the scope of the appended claims.

We claim:

1. A method for deep-drawing sheet metal parts by means of explosive, comprising the steps of placing the sheet metal part with the rim thereof on a support while leaving a hollow space therebelow corresponding in its size at least to the shape to be achieved,

arranging the explosive above the sheet metal part with an areal distribution at least sufiicient to extend to the inner rim of the support,

and detonating the explosive to permanently deform the sheet metal part freely into an unsupported final nonuniform shape corresponding to the areal distribution of the explosive.

2. The method according to claim 1, wherein the explosive has a detonation velocity that is smaller than the velocity of the sound within the sheet metal part to be deformed.

3. The method according to claim 2, wherein the detonation velocity of the explosive is at most equal to the velocity of one of the shearing and transverse waves in the sheet metal part to be deformed.

4. The method according to claim 1, wherein the detonation velocity of the explosive is at most equal to the velocity of one of the shearing and transverse Waves in the sheet metal part to be deformed.

5. A method for deep-drawing sheet metal parts by means of explosive comprising the steps of placing the sheet metal part with the rim thereof on a support while leaving a hollow space therebelow corresponding in its size at least to the shape to be achieved,

interposing a drawing die between the support and the sheet metal part, and arranging the explosive above the sheet metal part with a nonuniform areal distribution at least sufficient to extend to the inner rim of the support.

6. An arrangement for deep-drawing sheet metal parts by means of .an explosive, comprising:

support means,

at least one sheet metal part so supported onsaid support means as to leave therebelow a hollow space at least correspondingly larger than the form to be achieved for substantially free expansion of said part,

and explosive means arranged above the sheet metal part with an areal distribution that is sufiicient to extend at least up to the inner rim of said support means,

and antiwrinkle annular holder means loosely inserted between said sheet metal parts and said explosive means. 7. The combination according to claim 6, wherein the outer dimensions of said annular holder means are at least equally large as those of said sheet metal part.

8. An arrangement for deep-drawing sheet metal parts by means of an explosive, comprising:

support means, at least one sheet metal part so supported on said support means as to leave therebelow a hollow space at least correspondingly larger than the form to be achieved for substantially free expansion of said part,

drawing die means loosely inserted between said base means and said sheet metal part,

the outer dimensions of said drawing die means being at least as large as the outer dimensions of said sheet metal part,

and explosive means arranged above the sheet metal part with a nonuniform areal distribution that is sufiicient to extend at least up to the inner rim of said support means,

and antiwrinkle annual holder means loosely inserted between said sheet metal parts and said explosive means,

the outer dimensions of said die means and of said holder means being at least as large as the outer dimensions of said sheet metal part,

the inner dimensions of said holder means coinciding substantially with that of said drawing die means.

9. The combination according to claim 6, wherein the aperture in said annular holder means is filled with an inert material.

10. The combination according to claim 6, wherein said explosive means terminates substantially flush with the rim of said sheet metal part.

11. The combination according to claim 6, wherein said explosive means is distributed substantially uniformly.

12. The combination according to claim 6, wherein said explosive means is distributed substantially nonuniformly.

References Cited UNITED STATES PATENTS OTHER REFERENCES Explosive Forming of Honeycomb Sandwiches, by

Ida et al., Machinery, September 1963.

RICHARD J. HERBST, Primary Examiner. 

